Talking about efficiency, you should compile it on your own, using proper CFLAGS including march=native. So you need to do this on the target machine.
However be aware that certain NULL pointer bugs can crash shared libs whereas qvms are basically immune.
If you're really low on memory, I doubt that shared libs verus qvms will help. You should disable bots first and choose proper maps as well as a sane value for maximum clients.
Apart from that, the server has little to do in general, so I doubt you'll see a huge performance boost either way.
If qvms do not work with multiple server instances, they are simply setup wrong.